(1) Field of the Invention
The invention relates to codes represented by a number of bars which code is read by a reading head when the bars are illuminated.
(2) Description of Related Art
Such codes may be used on cartridges for injection devices so as syringes and pumps.
Patients who have to receive frequent injections often use a so-called pen injector by which wanted doses can be apportioned from a cartridge in the injector. When empty the cartridge can be replaced by a new full one. Another possibility is to use a so-called pump by which very small doses are infused with short time spacing. Also the pumps get the liquid to be infused from a changeable cartridge in the pump.
The cartridges have to carry printed information revealing the content of the cartridge. This information can be printed directly on the cartridge or on a label, which is glued to the cartridge. Further it is wanted that the cartridge carry a code defining a unique identification of the cartridge and its content and which code can be automatically read by a code reader. Such a code reader is appropriately mounted in the syringe or the pump using the cartridges, so that the code is automatically read when a cartridge is mounted in the injection device. This enables the injection device to display the information of the content of the cartridge on a display or to reject a cartridge containing medication, which was not prescribed or not meant for the injection device.
To enable visual inspection of the content of the cartridge such a cartridge is mainly made from a transparent material and a label with printed text and codes has to be at least partly transparent. The printed text leaves some place between the letters and between the lines and the text does not have to cover the whole surface of the cartridge.
Differently it is with the coding. To describe the problems we will look upon a commonly used cartridge which has the shape of a cylindrical glass tube which is at one end closed by a membrane which can be pierced by a needle through which the liquid in the cartridge can be pressed out by pressing a piston, which closes the other end of the tube, into said tube.
The code is commonly provided as a bar code having bars extending perpendicularly to the longitudinal axis of the cartridge. To ensure safe reading of the code maximum contrast between bars and spaces is aimed at. Consequently the bars are black opaque lines. A reader in the injection device reads this code when the cartridge is passed in its axial direction into the device. However, unless the rotational position of the cartridge is carefully watched during the mounting of the cartridge you cannot be sure that the bars of the code passes the reading field of the reader. Making the bars extend all the way around the cartridge will solve this problem but makes visual inspection of the content of the cartridge difficult in the part covered by the bar code. The code area may be restricted to the about 1 cm where the piston is positioned when the cartridge is full as inspection is not needed in this area.
For commercially available bar codes using ordinary printing technique on labels the minimum basic module corresponding to the thinnest bar or the smallest space is about 0.2 mm. Even with this fine basic module the 1 cm space will only leave space for very limited information. As a common bar code needs a number of start and stop bits, which informs the reader that a bar code is going to be read and further a number of check bits to provide sufficient redundancy to make the code insensitive to noise, the amount of information is further reduced.
Another source of failures which makes it impossible to use the fine basic module described above is the fact that it is difficult to wind the label around the cartridge with a sufficient precision. Where the edges of a label meet the ends of a bar may be displaced several tenth of a millimeter relative to each other. This calls for a coarser basic module for the bar code if errors shall be avoided when the reading of the bar code takes place along a line where the edges of the label meet.
An objective of the invention is to describe a machine-readable code for identifying the labeled content of cartridges, by which code the above-mentioned problems are avoided or mitigated.
This is obtained by a code represented by a number of bars which code is read by a reading head when the bars are illuminated, characterized in that the bars are mainly transparent and each along its whole length is provided with an optical grating which diffracts and reflects light impinging the surface carrying the code so that a minor part of this light is reflected and diffracted from the surface of a bar as a set of light beams of which beams at least one is chosen to be detected for the indication of the presence of said bar and the information stored in this bar when said bar is illuminated by a reading light.
A cartridge may carry a code represented by a number of bars mainly perpendicular to the axis of the cartridge, and the bars may be mainly transparent and each may along its whole length be provided with an optical grating which diffracts light impinging the surface carrying the code so that a minor part of this light is reflected diffracted from the surface of the bar as a set of light beams of which beams at least one is chosen to be detected for the indication of the presence of the bar when said bar passes a reading light field.
The reading may be performed by successive illuminating the bars when they pass a reading device during the insertion of the cartridge in a device using such cartridges.
When the bars are mainly transparent they may be distributed over the whole length of the cartridge without disturbing the visual inspection of the content of the cartridge and the better space which is thereby provided may be used for more information and for the provision of a larger space between the bars. The larger bars, and larger spacings between the bars, leads to reduced precision requirements for the optical parts of the reading head, which in turn allows for a low-cost construction of the reading head.
The optical gratings do not have to form an integral structure covering the bar. The bar may be composed of spaced stripes, dots or little islands carrying a grating and filling up the area of the bar where the spacing between the stripes, dots or little islands is smaller than the minor dimension of the reading light field.
The orientation of the lines of the grating may vary from bar to bar so that the planes defined by the sets of diffracted interference beams from different bars has different orientations.
If orientations are so chosen that each bar has a grating with one of two defined orientations, reflections from the bands may be interpreted as representing xe2x80x9c1xe2x80x9ds and xe2x80x9c0xe2x80x9ds in a binary code. When two defined orientations of the grating lines are used the two directions may appropriately be perpendicular to each other and be so oriented on the bars that they forms an angle of 45xc2x0 with the edges of these bars.
The grating may be provided as fine reflecting lines on the bars or by a corrugation in the bar areas of the surface of the material carrying the bars.
The corrugation may be provided as alternating ridges and grooves in the bar areas of the surface of the material carrying the bars.
The cross-section of the corrugation may have the shape of sinusoidal waves, square waves or saw tooth waves.
The bars may be distributed over the whole length of a cartridge, which may be a rotational symmetrical ampoule with bars having the shape of round going bands.
Especially when a cartridge is made of a plastic material the gratings may be made in the surface of the cartridge itself but may also be provided on a label, which is glued to the cartridge.
The code is described in connection with its use on cartridges for medical devices but may arbitrarily be used where a common bar code will deteriorate the appearance or impede inspection of the part carrying the code.